Field of the Invention
The present invention relates to a device for indication and adjustment of the operating tension of an endless chain strand of a chain conveyor which is equipped with a tensioning device modified for the generation of a pre-tensioning force.
Description of the Background Art
It is known that chain conveyors comprise of a strand of an endless chain which is formed by one, two, or even more chains running in parallel around at least one drive sprocket and trailing wheel. Carriers, such as flights, buckets etc., are attached to the chains. The chains most often lay on runners or run in channels. A chain conveyor comprises a working section and a reversing section, which can be placed one above the other or side by side. The entire working section of the chain conveyor is used for the transport of material, that is the transport section in the area between the feed hopper and the discharge point or discharge chute, or alternatively the entire working section plus a part of the reverse section between the feed hopper and the trailing wheel. Usually one of the sprockets is mounted in such a way that is can slide in the direction of the chain strand while this sprocket is coupled with a tensioning device, preferably a hydraulic cylinder or a screw mechanism. In some cases however, the pre-tensioning force adjusted by the tensioning device can change due to variations in resistance, especially in the case of a sticky transport material which accumulates on the sprockets, which lengthens the distance between them. Other sources of variation and thus the change in the actual operating tension of the chain strand are variable loading, changes in physical properties of the transported material, thermal expansion of the chain and the wear of function parts of the chain conveyor. It is possible to observe the changes in resistance or the change in operating tension in a real time with the necessary sensitivity, and to transmit it in a form of a control signal to the tensioning device. Therefore the tensioning device can be adapted for the immediate re-arrangement into a position generating the currently required pre-tensioning force.
From the document DE 20311436 U1, which corresponds to U.S. Pat. No. 7,117,989, an apparatus for reading the operating tension of an endless chain strand is known, comprising of a pivoting arm which is firmly mounted on a shaft which is pivoted by means of a bearing, arranged in the frame of the chain conveyor, in a direction perpendicular to the direction of the chain strand's movement. Outside the area of the transport section, according to said document, at the trailing wheel in the chain strand, there is arranged a concave section-where the contact point of said pivoting arm, rests and slides on the chain of the aforementioned chain strand. The shaft is coupled with the shaft angular displacement sensor. The signal from the shaft angular displacement sensor is transmitted to the control member, which is connected to the tensioning device fitted with a hydraulic cylinder. The amount of chain bending in the concave section is inversely proportional to the value of the pre-tensioning force. This means, that at higher pre-tensioning forces, the chain is less bent and vice versa. The pivoting arm responds quickly to changes in the chain's bending and even in the control member no delay occurs, and so the tensioning device is able to modify the size of pre-tensioning force according to the given selected algorithm without any time delay.
By means of the described apparatus for reading of the operating tension of the endless chain strand, it is possible, after its coupling with the tensioning device, to optimally fix the size of the actual pre-tensioning force, i.e. the operating tension of the chain strand. However the disadvantage of this particular apparatus is that it is only an indication device, that is to say it is not able by itself to vary the pre-tensioning force.